The present invention relates to various articles which contain as a main component a part in which a surface is coated with silver such as optically reflective members used in reflecting mirrors of photocopy machines, indoor and outdoor lighting appliances, automobile headlights, and the like, and to resin compositions for coating materials for silver. In more detail, the present invention relates to articles having a silver layer in which the anti-discoloring (anti-corrosion) properties are remarkably improved, and to resin composition for coating materials for silver with which it is possible to give to the silver a superior anti-discoloring (anti-corrosion) property.
The present application is based on Japanese patent application No. Hei 10-152751 filed in Japan, the content of which is incorporated hereinto by reference.
Silver has superior optical properties and electochemical properties, and has been used as a precious metal from ancient times for decoration, money, eating utensils, electric materials and materials for dentistry. In recent times, the use of silver in lighting appliances, photographic industry materials for photocopiers and the like, liquid crystal displays, semiconductor materials, conductive materials, and aerospace materials has increased rapidly. Silver is used widely as an industrial material.
However, the silver materials which are being put to these uses are extremely unstable chemically, and they react readily with sulfur dioxide gas, hydrogen sulfide, moisture, oxygen and the like in air to generate silver oxide, sulfides of silver, and the like. For this reason, there is the problem that silver surfaces discolor (corrode) to brown or black.
In addition, the discoloration (corrosion) of silver surfaces is further accelerated by high temperature environments, therefore, it has not been possible to use silver in parts such as the reflective mirrors of automobile headlights, the temperatures of parts of which exceed 150xc2x0 C. For this reason, aluminum is used in the reflective mirrors of automobile headlights.
However, silver whose surface has been made smooth is very good as a reflective material for light, and has a reflectivity approximately 10% higher than that of an aluminum surface. In addition, in lighting devices, generally, in order to concentrate the light and to match the polarity of the light, or in order for equalization of luminous and light diffusion, the light is repeatedly reflected, therefore, the difference between the total reflectance of silver and the total reflectance of aluminum is even greater. For this reason, the use of silver which is able to give higher lighting illumination from less electrical energy is desired.
On the other hand, as methods for preventing the discoloration (corrosion) of silver, methods of making alloys of silver with other metals such as copper, platinum, palladium, iridium, zinc, tin, and the like, and methods of applying a coating material such as epoxy resin or the like to the surface of the silver are known. However, in the former methods, there are problems with the malleability and ductility of silver becoming reduced, and the external appearance of the surfaces being degraded. With the latter methods, the adhesiveness of the coating material with the surface of the silver is unsatisfactory, and the durability of the coating material is unsatisfactory; therefore, it is difficult to prevent discoloration (corrosion) of the surface of the silver over a long period of time.
For this reason, in order for the silver to sufficiently exhibit superior ductility and malleability and obtain a surface having a glossy appearance, a search for a new type of coating material which has improved adhesiveness for the surface of silver and durability without relying on an alloy treatment became necessary.
The inventors of the present invention carried out careful research for a new type of coating material for protecting the surface of silver which had improved adhesiveness for the surface of silver and durability, and made a new invention related to a resin composition which can be used in coating materials. In addition, the present inventors have already presented coating materials having improved adhesiveness for the surface of silver and durability in Japanese Patent Application, First Publication No. Hei 06-57198; Japanese Patent Application, First Publication No. Hei 08-245903; Japanese Patent Application, First Publication No. Hei 09-241532; Japanese Patent Application, First Publication No. Hei 10-158572; and Japanese Patent Application, First Publication No. Hei 10-292152.
However, in high temperature environments, there are still situations in which the surface of the silver becomes discolored (corroded) even when these coating materials are used. Furthermore, in uses in which the surface of the silver is exposed to temperatures of around 200xc2x0 C., there is the problem that the coating material turns yellow and hinders the reflecting properties of the silver. For this reason, additional effective strategies for increasing the protective properties for silver surfaces are demanded.
As the result of careful research in view of these circumstances, the present inventors discovered that for the prevention of discoloration (corrosion) of a silver layer laminated as a thin layer onto the surface of a substrate, the protection of the contact surface of the silver layer and the substrate is essential, and that protection of only the reflective surface of the silver is inadequate. Furthermore, they discovered that ingenuity is required in the selection of materials for the formation of a protective layer on the substrate side. In addition, the present inventors discovered that it is possible to obtain a resin composition for coating silver which has superior heat resistance and does not turn yellow even when exposed to temperatures of around 200xc2x0 C. by means of using a multi-functional silicone cross-linked resin having a siloxane component as a main chain.
In more detail, in the article having a silver layer of the present invention, a first cured coating layer (A) comprising a resin composition in which a resin having anti-corrosion properties for silver and adhesiveness for both a substrate and silver, or a metal comprising silver as a principal component, is formed on the surface of the substrate;
a silver layer (B) comprising silver or a metal comprising silver as a principal component is formed on this first cured coating layer (A); and
a second cured coating layer (C) having heat resistance and transparency and comprising a resin composition comprising as a principal component at least one type of resin selected from the group consisting of
a silicone acrylic resin (c1),
a silicone alkyd resin (c2), and
a multi-functional silicone cross-linked resin (c3) formed on the silver layer (B). This multi-functional silicone cross-linked resin (c3) has an average compositional formula represented by general formula I, a number average molecular weight of 500xcx9c1000, and a main chain formed by siloxane bonds:
RnSiO(4xe2x88x92n)/2xe2x80x83xe2x80x83(I)
(in the formula, R is a hydrogen atom, a lower alkyl group, a phenyl group, or a substituted phenyl group; and n is a number from 1.2 to 1.4).
By means of the above, an article having a silver layer with superior anti-discoloration (anti-corrosion) properties can be obtained.
In addition, it is preferable for the resin which forms the above-mentioned first cured coating layer (A) to be at least one type of resin selected from the group consisting of a silicone acrylic resin (c1), a silicone alkyd resin (c2), and a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by the above-mentioned general formula I, a number average molecular weight of 500xcx9c1000, and a main chain formed by siloxane bonds. Thereby, an article having a silver layer with superior anti-discoloration (anti-corrosion) properties can be obtained.
In addition, it is preferable for the resin which forms the above-mentioned second cured coating layer (C) to be a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by the above-mentioned general formula I, a number average molecular weight of 500xcx9c1000, and a main chain formed by siloxane bonds. Thereby, it is possible to obtain an article having a silver layer in which the second cured coating layer (C) does not turn yellow even when exposed to temperatures of around 200xc2x0 C.
In addition, the above-mentioned substrate is preferably metal or synthetic resin. Thereby, the article having a silver layer sufficiently exhibits the effect of anti-discoloration (anti-corrosion).
In addition, the above-mentioned silver layer (B) is preferably a thin layer of silver or mainly silver formed by a vacuum deposition method, an ion plating method, or a sputtering method. Thereby, the article having a silver layer sufficiently exhibits the effect of anti-discoloration (anti-corrosion).
In addition, the article having a silver layer of the present invention preferably has a specular glossy surface or reflective surface. Thereby, it is possible to obtain an article having a silver layer suitable for a light reflecting member for a reflecting mirror of a copy machine, indoor or outdoor lighting appliances, and automobile headlights.
In addition, since the article having a silver layer of the present invention sufficiently exhibits the reflectance property of silver, it can be effectively used in reflective mirrors for indoor or outdoor lighting appliances and the reflective mirrors of automobile headlights.
The resin composition for coating materials for silver of the present invention contains a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by general formula I, a number average molecular weight of 500xcx9c1000, and a main chain formed by siloxane bonds.
RnSiO(4xe2x88x92n)/2xe2x80x83xe2x80x83(I)
(In the formula, R is a hydrogen atom, a lower alkyl group, a phenyl group, or a substituted phenyl group; and n is a number from 1.2 to 1.4.)
Thereby, it is possible to obtain a resin composition for coating materials for silver which has superior heat resistance, gives a superior anti-discoloration (anti-corrosion) property to silver and the film of which does not turn yellow even when exposed to high temperatures of around 200xc2x0 C.
In addition, it is preferable for the resin composition for coating materials for silver of the present invention to additionally contain silver deactivators, in particular, complexes of zirconium with carboxylic acids. Thereby, it is possible to obtain a resin composition for coating materials for silver which reliably gives a superior anti-discoloration (anti-corrosion) property to silver.
In addition, it is preferably for the coated silver to be a thin layer of silver or mainly silver formed by a vacuum deposition method, an ion plating method, or a sputtering method. Thereby, the effect of giving an anti-discoloration (anti-corrosion) property to the silver is sufficiently exhibited.